Conventionally, as an intake parameter-calculating device for an internal combustion engine, one disclosed in Patent Literature 1 is known. This intake parameter-calculating device calculates a demanded intake pressure P as an intake parameter, and is equipped with an air flow meter, an intake pressure sensor, a throttle sensor, and so forth. In the intake parameter-calculating device, an accelerator pedal opening Acc, which is an operation amount of an accelerator pedal, is calculated based on a detection signal from the throttle sensor, an actual intake air amount Gact is calculated based on a detection signal from the air flow meter, and an actual intake pressure Pact is calculated based on a detection signal from the intake pressure sensor.
Further, a demanded shaft torque is calculated using the accelerator pedal opening Acc and the rotational speed NE of the engine, and the demanded intake pressure P is calculated using an intake system model expressed by an equation (3), which defines the relationship between the demanded shaft torque and the demanded intake pressure P. The intake system model is derived from the equation of state of gas, and includes a learned value Kn as a multiplication coefficient. The learned value Kn modifies a modeling error, and is calculated by average calculation (weighted average calculation) of an immediately preceding value and a base value Knbase of the learned value Kn. The base value Knbase is calculated by dividing a ratio between the actual intake pressure Pact and the actual intake air amount Gact by a ratio between the demanded intake pressure P and a demanded intake air amount G calculated based on the intake system model.